Automobile speed control



July '15, 1969 R. w. CARP l-:TALv 3,455,411

l AUTOMOBILE SPEED CONTROL 5 Sheets-Sheet 1 Filed OCT.. 24, 1967 @mmf nw 3 Sheets-Sheet 2 R. W.`CARP ETAL AUTOMOBILE SPEED CONTROL July 15,1969 Filed oct. 24, 1967 ATTORNEY July l5, 1969 R. w. CARP Erm.

v AUTOMOBILE SPEED CONTROL 5 Sheets-Sheet 5 Filed Oct. 24, 1967 FIG. 3.

SYSTEM PERFORMANCE CHARACTERISTICS m D m MN E GPwwM NDH .ANH/ I .S .EmwMa MMA LH @Mmm RWM 4%;ME5/M ATTORNEY United States Patent O U.S. Cl.180-105 26 'Claims ABSTRACT F THE DISCLOSURE A automobile speed controlsystem wherein a voltage proportional to actual vehicle speed is fedthrough a lowloss memory capacitor to a comparator high input impedanceport, momentary referring of which to a predetermined voltage impressesthe vehicle instantaneous speed across the capacitor in the form of acommand speed voltage. Thereafter, changes in vehicle speed cause thevoltage at the comparator input port to change in accordance therewith,although the voltage across the capacitor remains constant. A voltageproportional to throttle position is applied through a feedback shapingcircuit to the second comparator input port. The feedback circuitutilizes a D.C. feedback circuit paralleled by an A.C. feedback circuitto increase the throttle feedback signal when the throttle is moving.The error signal developed in the comparator is amplified and applied toa vacuum modulator which controls the pressure in a vacuum motor which,through a linkage, positions the throttle. A capacitor and resistancenetwork may be switched into the comparator so as to vary the high inputimpedance port circuit voltage proportional to actual vehicle speed inaccordance with the time constant of the network in such a manner as tocause the apparent vehicle speed to decrease, thereby causing thevehicle to accelerate at a predetermined rate. Control system turn-olfcircuitry is provided which temporarily disables the error signalamplifier whenever a turn-off voltage is applied thereto. This turnoffvoltage may be applied by an operator controlled switch whichsimultaneously places the memory capacitor in condition to record theinstantaneous vehicle speed in the form of a command speed signal whenthe turn-off voltage is removed, thereby allowing the operator to causethe vehicle to decelerate to a new, lower command speed. Turn-offvoltage may also be supplied through a brake operated switch. Thecontrol system is programmed to respond to voltage levels which arecaused to appear at a system control point whenever the control point isshunted to ground through various resistances. These resistances aremounted on the vehicle steering column, thereby allowing all operatorinitiated functions to be controlled through a single wire.

Cross references to related applications This invention employs severalcomponents of the type generally disclosed in pending application Ser.No. 550,744, filed May 17, 1966 now Patent No. 3,381,771 and Ser. No.597,789, filed Nov. 29, 1966 which are assigned to the assignee in thepresent application.

Background of the invention Electronic automobile speed control systemshave been disclosed wherein an electrical signal proportional to actualvehicle speed, an electrical signal proportional to a command vehiclespeed, and an electrical signal proportional to throttle position arecombined to generate an error signal which is applied to position thethrottle so as to make actual vehicle speed equal to command vehiclespeed. Further improvements have Patented July 15, 1969 ICC beendisclosed which utilize a memory in the form of low-loss capacitor whichcouples the actual vehicle speed signal to a high input impedance portof the error signal generator. The command speed signal is stored in thememory by momentarily referring the common terminal between the memoryand error signal generator to a given voltage, the command signal beingthe instantaneous magnitude of the actual vehicle speed signal. Logiccircuits were also disclosed which inactivate the speed control systemwhenever the automobile brakes are applied. The commercial success ofthese electronic speed control systems has been due to theirconvenientlyA small size and low cost. It is now desired to furtherimprove the electronic speed control systems so as to accomplishfunctions heretofore impossible to be performed by other systems.

Summary of the invention Accordingly, an improved electronic automobilespeed control system with a memory for recording command speed has beendevised. Circuitry has been added to the memory to cause the apparentactual vehicle speed signal to indicate a decrease in vehicle speed inorder to cause the vehicle to accelerate when the operator so desires.Additional circuitry has been added to cause the vehicle to deceleratewhen the operator so desires. At the end of the accelerate or decelerateperiod the then actual vehicle speed signal is impressed automaticallyon the memory as a command speed signal.

Fail-safe circuitry has been incorporated into the speed control systemof this invention which prevents actuation of the system whenever opencircuit failures occur in the brake harness. Another fail-safe circuitautomatically deactivates the control system whenever actual vehiclespeed drops substantially below command speed, thereby providing aredundant deactivating signal should the system deactivating signal,normally produced byV a brake switch at the instant the brakes areapplied, fail.

A special feedback circuit having both A.C. and D.C. feedback paths hasbeen inserted int-o the control system. This produces a moving throttleposition feedback signal approximately twice the magnitude of thethrottle feedback signal when the throttle is stationary resulting insmoother pull-in of the throttle when the control system is activatedand resultant closer speed control.

Operator controlled functions of the speed control systern are initiatedby switches which are most conveniently located on the steering wheel orthe steering column. Normally, the increased versatility of the presentsystem would require extensive wiring between the steering wheel mountedswitches and the electronic package which is most conveniently locatedat the fire wall or under the hood; however, a level switching circuithas been added which basically includes a number of transistors whichare programmed to initiate the various functions of the speed controlsystem in response to a voltage appearing at a common control point.This voltage is applied through a single Wire between the control pointand the steering wheel mounted switches, the various switches beingactuated by the operator to set up the proper predetermined voltage atthe control point.

Brief description of the drawings FIG. l is a functional block diagramof the speed control system of the invention;

FIG. 2 is a schematic diagram of the electronic control circuitry shownin block form in FIG. 1; and

FIG. '3 is a plot of curves showing the performance characteristics of atypical system.

Description of the preferred embodiment Referring to FIG. 1, a sensor 16is connected into the speedometer cable and driven at the same speed asthe speedometer. Since the gear ratio between the drive wheel and thespeedometer cable is xed, the sensor output frequency is proportional tothe automobile speed. The sensor drives a counter 181, which generates aD.C. voltage level proportional to the same signal input frequency. Theoutput of counter 18 is, therefore, a D.C. voltage level proportional tovehicle speed. The counter output drives through memory 19 into a highinput impedance comparator 20. The vehicle operator can impress acommand speed signal proportional to the instantaneous speedometerindicated speed of the automobile by momentarily depressingset/accelerate pushbutton 38y or set/coast down pushbutton 39 of levelswitching circuit 35. Pushbuttons 36, 37, 38, `39 and 40 are normallymounted directly on the steering wheel. It will be noted that speedcontrol pushbuttons 37, 38, 39 and 40 initiate four separate speedcontrol functions, in a manner to be described later, yet require only asingle wire 35B leading from the steering wheel 35A to a remotelylocated portion of the level switching circuit 35C.

Once a command speed signal has been impressed across memory 19 anyvariations in vehicle speed will cause the voltage on line 21 to vary inaccordance therewith. A feedback potentiometer 55, mechanicallyconnected to throttle linkage arm 48, provides a signal voltageproportional to the position of throttle linkage arm 48. This feedbackvoltage is fed back through the feedback circuit 56, which, as has beenstated, passes a feedback voltage, when the throttle is moving,approximately twice the magnitude of the stationary throttle feedbackvoltage. The feedback voltage is applied through line 23 to the secondinput port of comparator 20. The resultant error signal is amplified inamplifier 26, the output of which is used to control a vacuum modulatorcomprising solenoid Valves 221 and 222 which in turn control thepressure on one side of diaphragm 41 of vacuum modulator and actuator28. Briefly, the solenoid valves include needle valves 31 and 32 whichare positioned against ports 33 and 27, respectively. In accordance withthe proper driver signal either valve 31 opens so as to allow a vacuumto be drawn by vacuum storage tank 51 in modulator chamber 28B, oralternately to allow needle valve 32 to open, thereby allowingatmospheric pressure to enter chamber 28B through port 27.

The vacuum actuator includes exible diaphragm 41 which divides themodulator and actuator into chambers 28A and 28B. Chamber 281B is leaktight and communicates in the aforementioned manner, either to theatmosphere through port 27 or to vacuum storage tank 51 through port 33.Chamber 28A is open to the atmosphere through port 218C. Spring 42 isdisposed in chamber 28B and tends to urge diaphragm 41 and connectinglinkage 47 to the right or to a position of engine idle. Throttle crankd is urged to the right by spring 52, tending to abut linkage arm 48, soas to rotate throttle 419 t0 a position of engine idle. While the speedsystem is operating, chamber 218B is exposed to sub-atmospheric pressureby the closing of valve 32 and the opening of valve 31. Diaphragm 41moves into chamber 28B, compressing spring 42 until the reduced pressurein chamber 28B plus the spring pressure equals atmospheric pressure.Linkage 47 with arm 48 are carried by diaphragm 41 to force abuttingcrank 50 to the left, opening throttle 49. 1t may be readily seen thatan operator, at any time, may increase speed by depressing theaccelerator pedal. When the accelerator pedal is released, crank 50 willfall against linkage arm 48 and the speed control system will regaincontrol.

A brake switch 110, which is closed when the brakes are applied, appliespositive A+ voltage through brake harness fail-safe circuit 60 to logiccircuit 25 which contains certain control transistors which areback-biased and turned off by this A+ voltage. The speed control systemis thereby deenergized so that solenoid valve 32 opens and valve 31closes allowing atmospheric air to enter chamber 28B, thereby returninglinkage 47 to a position of engine idle. In like manner, brake harnessfail-safe circuit 60 allows the A+ voltage to be transferred directly toline 60B whenever a failure in the brake harness occurs. Thus, in amanner identical to the shutting down of the speed control system by theclosing of switch 110, the system is shut down whenever the brakeharness fails.

Referring to FIG. 2, sensor 16 may suitably be a variable reluctancealternating current type generator providing a signal having a frequencyvarying directly as the rotor speed and consequently as the automobileroad speed. A linear transistor 79, normally biased into saturation byresistor 76, receives the output of sensor 16 through temperaturecompensating diode 75. Negative half-cycles of the output of sensor 16bias transistor 79 non-conductive. The output of transistor 79 thereforeconsists of positive pulses of fixed amplitude with the frequencyproportional to automobile road speed. These speed pulses are applied tothe counter circuit of the energy storage type comprising diodes 82 and83 and capacitors 81 and 819. A voltage proportional to actualautomobile road speed appears across capacitor 89, shunted by resistor84 and temperature compensating diodes 86 and 87, forward biased byresistor 88.

Feedback potentiometer 55, which is connected along with resistors 142and 137 across the A+ regulated voltage, supplies a voltage proportionalto throttle position through a feedback circuit 56 as shown at FIG. l.D.C. voltages generated by the feedback potentiometer, such as would begenerated when the throttle is not moving so that the potentiometer armis stationary, pass through resistor 56 to the gate of eld effecttransistor 96. A.C. voltages generated by the feedback potentiometer,such as would be generated when the wiper ar-m is moving, also passthrough the aforementioned D.C. path, but also through the pathcontaining capacitor and resistor 61. In a manner to be made clear, thefeedback circuit operates to prevent too rapid movement of the throttlewhen vehicle speed is greatly below command speed, while at the sametime allowing greater sensitivity of the comparator to the feedbacksignal as the vehicle attains command speed.

A low leakage loss memory capacitor 91 is connected between the inputterminal of capacitor 89 and the gate connection of eld eifecttransistor 95. Field effect transistors are characterized by theirextremely high gate impedance, so that memory capacitor 91 isessentially open-circuited at the transistor gate connection. Point c ismaintained at a low positive voltage potential by the voltage dividerconnected to the A+ voltage and comprised of resistors 154, 155 and 102.If point a is now connected to point c by a momentary closing of switchcontacts 104 and 105, a voltage is impressed across the memory capacitor91 equal to the voltage at that instant across capacitor 89, less thesmall voltage at point c. Since the voltage across capacitor 89 at theinstant contacts 104 and 105 open is proportional to the automobilespeed at that instant, a command speed voltage essentially proportionalto actual vehicle speed at the instant the contacts open is impressed onmemory capacitor 91. Since the memory capacitor is connected to the highimpedance gate circuit of transistor 95, the command speed voltageimpressed on memory capacitor 91 will remain practically constant afterthe contacts open. If the automobile speed also remains constant afterthe contacts 104 and 105 open, then the voltage at point a will remainconstant and equal to the voltage at point c. If thereafter theautomobile speed decreases, the voltage across capacitor 89 willdecrease and the voltage of point a will decrease a proportional amount.

Field eifect transistors 95 and 96, and resistors 93, 97 and 98 comprisea comparator in the form of a differential amplifier. Comparator outputerror signal is taken from the drain terminal of transistor 95 andapplied to the base of transistor 150 and to the base of transistor 130.Transistors 150, 160, 190, 200 and 210'comprise an amplifier whichamplifies the error signal with amplifier feedback being provided fromthe emitter of transistor 190 to the base of transistor 160` through theparallel combination of resistor 172 and capacitor 173. Transistor 150is differentially connected with transistor 155 to increase the gain ofthis amplifier stage and to provide temperature compensation. Transistor155 is biased conductive by resistors 152, 153, 154, 155 and 102. Theconstant voltage divider comprising resistors 154, 155 and 102 combinedwith the essentially constant diode drop across transistor 155 permitthe differential amplifier emitter voltage to remain constant. Theemitter of transistor 200 is connected to the collector of transistor210 through diode 214, while transistor 210 emitter is connecteddirectly to ground. The amplified error signal appears on the base oftransistors 200 and simultaneously through resistor 215 to the base oftransistor 210. Diode 214 is back biased until transistor 210 conducts;however, transistor 200 will also be cut-off until its base voltageexceeds diode 214 forward conduction voltage plus the saturation voltageof transistor 210 and its own base emitted forward voltage. Therefore,as the error signal increases transistor 210 will allow vent winding 221to energize and close normally open vent valve 32. As the error signalincreases, further, transistor 200 will allow vacuum winding 222 toenergize, thereby opening normally closed vacuum valve 31, causing airto be drawn out of chamber 28B shown at FIG. 1. Diaphragm 41 moves tothe left, carrying linkage 47 and arm 48 which abuts throttle crank 50,thereby causing throttle 49 to pivot to a more open position. Of course,as the error signal thereafter decreases, a reverse action takes place.The vacuum valve closes, 'trapping the then acquired vacuum in chamber28B. The back developed by the decay voltage across winding 222 isshunted by diode 194. As the error signal further decreases, indicatingthat vehicle speed is greater than command speed, vent valve 32 willopen, bleeding chamber 28B, causing diaphragm 41 to move to the right,to a position to cause throttle 49 to move to a less opened position.Similarly, back thereby generated is shunted through diode 196.

Assuming now that ignition switch 61 has been closed so that voltageregulated by Zener diode 170 appears through resistor 90 on line 80, thespeed control system is turned on by momentarily depressing steeringwheel mounted switch 37 thereby applying A+ voltage across horn relay36A, resistors 226, 227 land 229, and relay winding 330. The voltagedrop -across horn relay 36A is not sufficient to energize it, however,relay winding 330 has suiiicient turns to energize that relay, closingcontacts 333, A+ voltage now being supplied through these contacts tothe relay winding, thereby latching the relay in a closed condition. Itwill be noted that when switch 37 was depressed, A+ voltage, less thedrop through horn relay 36A, appeared at control point 335, biasingtransistors 340 and 345 off. After switch 37 is released and contacts333 are latched closed, A+ voltage remains at control point 335, therebycontinuing to bias these transistors off.

The `actual vehicle speed signal appearing across capacitor 89 isapplied to the base of multipurpose transistor 145, lwhich in this caseis operating as an amplifier, the output of which is taken lfrom thecollector and applied to the base of turn-on transistor 180. Diode 140allows the amplifier comprising transistor 145 to change gain at acritical value of transistor base voltage as follows. At low values oftransistor base voltage, corresponding to low automobile speed,transistor 145 collector voltage is high. Thus diode 140 is back-biased,so that the gain of the amplifier stage depends on the transistoremitter and collector resistors 137 and 156. In a practical circuit,resistor 156 was approximately twenty times larger than resistor 137resulting in an amplifier gain of 20. As transistor voltage increasesfurther, indicating an increasing automobile speed, the transistorbecomes more con-ductive and its collector voltage drops until diode 140fbecomes forward biased. Resistor 156 is now paralleled by resistor 142,thereby causing the amplifier gain to drop in accordance therewith. Inthe practical circuit, resistor 142 was approximately equal to resistor141 so that the amplifier gain dropped to unity. The significance ofmaking resistor 142 of slightly different value than resistor 141 willbe shown later. The circuit elements are chosen so that at apredetermined automobile speed, known as threshold speed, diode 140becomes forward biased and transistor base voltage reaches a criticalvalue, thereby `arming transistor 180 so that if A+ voltage were appliedon line 341, transistor 180 would be sutliciently conductive to energizecoil 181.

If the vehicle is above the threshold speed and the speed control systemis on (contacts 333 closed) the operator may tap-set the then Kacquiredvehicle speed into the system memory so as to allow the system tomaintain vehicle speed automatically. To do so, the operator momentarilydepresses either set/accelerate switch 38 or set/coastdown switch 39.Assuming that the operator taps set/accelerate switch 38, voltage oncontrol point 335 is determined, while the switch is closed, by thevoltage divider consisting of resistors 226 and 38A. This voltage isstill too high to permit transistor 345 to turn on, however, theadditional voltage drop through resistor 228 lowers transistor 340 basevoltage sufiiciently so that this transistor saturates. A+ voltageappears on line 343 and is impressed through diode 182 and relay winding181 to the emitter of transistor 180, whose base voltage it will beremembered, has reached a critical threshold value, which value is suchas to cause transistor 180 to now turn on sufficiently to energizewinding 181, causing relay contacts 184 to close, thereby latching therelay in the energized condition due to the A+ voltage `supplied overline 343. As long as the vehicle remains over the threshold speed, sothat transistor 180 remains conductive, contacts 184 will remainlatched, unless OFF lbutton 40 is depressed, the action of which will beexplained below.

Simultaneously with the latching of contact 184, the initial voltagepulse on line 341 causes a voltage determined by resistors 352 and 353to energize relay windings 351. In like manner relay winding 349 isenergized through capacitor 348, but the winding is deenergized once thecapacitor is charged. Since the operator has merely tapped the set/accelerate switch 38, the switch opens almost immediately, once morecausing a voltage pulse to pass across capacitor 348 to energize relaywinding 349. Winding 349 controls contacts 104 while winding 351controls contacts 105. Since the voltage across winding 351 is less bythe drop through resistor 352 than the drop across winding 349, contacts105 will open first upon release of switch 38, followed shortly by theopening of contacts 104. The significance of this contact operationsequencing will be apparent when the operation of the acceleration andcoast-down circuits is discussed. It will be noted, that with bothcontacts 104 and 105 closed, point a is connected to point c, and whencontacts 105 open, a commond speed voltage equal to the voltage acrosscapacitor 89 is now trapped across capacitor 91.

lf the operator wishes to have the speed control system cause thevehicle to accelerate, he depresses the set-accelerate switch 38 andholds it down until the vehicle has accelerated to the desired speed.Release of this switch will then impress a command signal correlative tothe then acquired actual vehicle across memory capacitor 91 as follows.When switch 38 is depressed, transistor 340 saturates as aforementioned,latching contacts 184 if not already latched and energizing winding 349and 351, thereby causing contacts 104 and 105 to close. As before,winding 349, which is connected to positive D.C. voltage throughcapacitor 348, deenergizes as soon as capacitor 348 is charged, openingcontacts 104. The gate of iield effect transistor 95 is now connected toground through the network consisting of capacitors y85 and 91 andextremely large resistor 103. The charge on the gate, therefore, slowlyleaks to ground. The error signal increase in accordance therewith andthe automobile accelerates, increasing the voltage across capacitor 89.Upon release of switch 38, winding 330 once more becomes energized,closing contacts 104, thereby connecting point a to point c. This is thespeed setting mode of the speed control system. Because of theaforementioned greater sensitivity of winding 349 over 351, winding 351first deenergizes causing contacts 105 to open, thereby completing thesetting of the speed command signal across capacitor 91. Winding 349then deenergizes, opening contacts 104.

If set/ coast-down switch 39 is depressed and held down, bothtransistors 340 and 345 are biased into saturation. Saturation oftransistor 340 causes an effect similar to that caused when set/accelerate switch 38 is depressed. Additionally, the saturation oftransistor 345 causes a positive voltage to appear on line 344 and henceon the base of transistor 160, causing that transistor to saturate,thereby back biasing transistors 190, 200 and 210 which cause windings221 and 222 to become deenergized. Vacuum valve 31 closes and vent valve32 opens, venting the vacuum actuator, causing linkage 47 of FIG. l tomove to the right or a position of engine idle. The vehicle then coastsdown. If the operator releases switch 39 while the vehicle is above thethreshold speed, the then acquired speed will be set across the memorycapacitor in the form of a command speed signal as follows. Upon releaseof switch 39, positive voltage on lines 341 and 344 disappears almostimmediately; however, due to the aforementioned greater sensitivity ofwinding 349 contacts 105 open before contacts 104 thereby setting thecommand speed.

When switch 40 is depressed, control point 335 is grounded so that thevoltage at point e assumes a value equal to the diode drop of transistor345. The voltage across winding 330 is no longer sufficient to hold thatwinding energized so previously latched contacts 333 open, therebyturning off the speed control system.

Brake switch 110 is ganged to the vehicle braking system and is closedwhen the brakes are applied. With switch 110 closed, a positive voltageis applied through resistor 119 to the base of transistor 160 so as toturn-off the entire control system in a manner identical to theturning-olf of the system when a positive voltage is applied totransistor 160 base by the closing of switch 39. Additionally, apositive voltage is applied through diode 122 to the base of transistor180, causing that transistor to turn olf and unlatch contacts 184.

If upon application of the vehicle brakes, switch 110 should fail toclose or in another manner, the speed control system should continue tofunction, a redundant, failsafe system disable network would bedesirable. As the vehicle slows down in response to the braking actionon the vehicle, the system error signal increases with resultant openingof the throttle. With the throttle wide open, so that the wiper ofthrottle feedback potentiometer 55 is completely toward the groundposition, and the vehicle continuing to decelerate under the action ofthe brakes, transistor 95 will turn off causing its drain voltage tosuddenly rise thereby turning off normally conductive transistor 130,its collector voltage dropping in response thereto. Since transistor 130collector is connected to transistor 185 base, the later transistor willturn off, interrupting the current flow through Winding 181 so as tounlatch contacts 184.

An additional fail-safe circuit which prevents operation of the systemwhenever the brake harness comprises line 118 and resistor 117.Normally, the voltage on line 60B is shunted to ground through brakelights or relay 112 so that diode 122 is not forward biased and thevoltage of the base of transistor 160 supplied through resistor 119 isinsuicient to affect that transistor. If now the brake harness shouldopen, the voltage on line 60B Will rise and the system will turn olf ina manner similar to the turn-0E caused by closing switch 110. Normally,with the brake harness in tact and brake switch open, the current owthrough the harness will be insuicient to energize the brake light.

Diodes 62 and 113 and capacitor 116 prevent damaging line surges whichmay occur.

It will be remembered that the frequency generated by sensor 16 islinearly proportional to actual vehicle speed. The voltage developedacross capacitor 89, however, which is the voltage proportional toactual vehicle speed, is not linearly dependent thereon due to theinherent nonlinearity of the charge-storing circuit. Multipurposetransistor provides a means of varying the throttle feedback signal inresponse to vehicle speed to compensate for this non-linearity. Theemitter to collector circuit of transistor 145 is connected acrossthrottle feedback potentiometer 55, while a voltage proportional toactual vehicle speed is impressed on its base. As vehicle speedincreases, increasing base voltage, this transistor becomes moreconductive, decreasing the voltage across the potentiometer, hence alsodecreasing the available throttle feedback. By proper design, theroll-olf of the throttle feedback can be made to compensate for theroll-off of the electrical signal proportional to vehicle speed.

It is also desirable, as will Vbe shown, to provide a higher averagefeedback voltage at higher speeds for a given wiper position. As waspreviously explained, resistor 142 is slightly different in value thanresistor 137. If resistor 142 is smaller and the potentiometer wiperposition corresponding to engine idle is at the mid-point of thepotentiometer winding, the average feedback voltage for a given wiperposition will rise as speed increases in addition to a compression ofthe available total feedback voltage range. This increase in averagefeedback voltage could also be attained, if it was desired to makeresistors 142 and 137 equal, by shifting the potentiometer wiper arm foridle engine throttle up, or in any other manner causing the resistancebetween wiper arm and line 80 to be less than the resistance from thewiper arm to ground at idle engine throttle so long as the other designcriteria are met.

FIG. 3 illustrates the throttle feedback characteristics of the controlsystem. For the purpose of interpreting the ligure, ideal actual speedis defined as the speed an ideal automobile would attain at steady stateconditions with a given throttle opening under unvarying engine loadingand driving conditions. Curve B is a plot of ideal actual speed versusD.C. feedback voltage at point b of FIG. 2 and illustrates thenon-linearity of throttle setting compared with automobile speed` TheD.C. feedback voltage at point b, of course, is indicative of throttleposition. Curve A is a plot of actual speed less command speed versusvoltage at point a on FIG. ,2 and is used as a transfer curve inconjunction with curve B. Vc is the voltage at point c. From theprevious discussion, it is apparent that the system can attainequilibrium only when the voltage at point a equals the voltage at pointd while the throttle is stationary, that is, where constant voltage(vertical) lines intersect curves A and B.

To illustrate more fully the operation of the control system andfeedback network an example will be given. Assume that an ideal vehicleis moving at 70 m.p.h. under unvarying engine loading and drivingconditions with the control system inactivated. Linkage 47 and arm 48are in a position of engine idle while the operator has overridden thesystem to position the throttle to maintain 70 m.p.h. Throttle feedbackpotentiometer wiper, which is ganged to arm 48, is also in a position ofengine idle (point r on FIG. 3). The operator now momentarily depressesthe set/ accelerate switch, thereby setting voltage Vc at point a ofFIG. 2. If the feedback circuit were purely resistive and properlyscaled, voltage at point b would move along curve B toward voltage Vc.The difference in voltage between the potentials at points a and bdetermines the magnitude of the error signal. It should be obvious thatwith a purely resistive throttle feedback network, the error signalbecomes very small as point b voltage approaches point a voltage. Thenew feedback network provides a means of increasing the throttlefeedback before equilibrium conditions are attained thereby affordingsmoother pull in of the throttle. Assuming again the conditions of thefirst example except that a throttle feedback network as shown in FIG. 2is used. As the throttle linkage 47 and arm 48 start to pull in throttlefeed-back voltage will follow along curve C which illustrates theincreased throttle feedback signal from the moving feedbackpotentiometer wiper. When throttle feedback voltage reaches s the systemis apparently balanced, the error signal goes to zero and the throttleand wiper movement cease. The A.C. component of throttle feedbackdisappears so that throttle feedback voltage moves toward curve B,thereby causing an error signal to be generated indicating the throttlehas opened too wide so that the control system now attempts to decreasethe throttle opening. The Athrottle feedback voltage will thereafterfollow the generally sinusoidal curve from s' to s where equilibrium isfinally attained.

Ideally constant driving conditions have been assumed. In actualoperation, an automobile encounters a wide variety of drivingconditions, such as wind from various directions, hills, curves andrough roads. If the automobile now starts up hill, the speed willdecrease causing the voltage at point a to fall. This will tend to openthe throttle further. Movement of the throttle linkage and arm increasethe A.C. feedback producing an apparent indication of the throttle beingless open than it actually is. The error signal is therefore larger thanwould -be possible with a resistive feedback network.'In this manner,smoother control is attained while the system assumes a new equilibriumposition. If the loading caused by the hill is equivalent to l m.p.h.additional throttle opening, the throttle must open to a new positionequivalent to 80 m.p.h. ideal actual speed to maintain 70 m.p.h. Thevoltage at point b of FIG. 2 will therefore drop to Vt. Vt on curve Acorresponds to an actual speed less command speed of -0.3 m.p.h. so thatactual speed will drop to 69.7 m.p.h. to maintain the system inequilibrium. A reverse process occurs when the load on the automobiledecreases, such as when the automobile goes down hill. less throttleopening is required to maintain speed and actual speed must increaseslightly to maintain equilibrium.

It will now be remembered, that the range of the feedback potentiometeras well as the value of the feedback voltage for a given throttleopening is responsive to the actual speed of the vehicle. Under theaforementioned ideal conditions, the throttle opening required tomaintain the ideal vehicle at a speed of 70 m.p.h. produces a D C.feedback voltage at point b of FIG. 2 equal to point c voltage. Thevehicle is now controlled at 70 m.p.h., the system operating to maintainspeed as previously described.

If the system is activated under ideal conditions while the idealvehicle is moving at 5() m.p.h., transistor 145 Would act to extend thepotentiometer range While lowering the average feedback voltage. Athrottle opening for an ideal speed of 70 m.p.h. in the previous exampleproduced equilibrium. However, the lowering of the average feedbackvoltage means that the throttle need not open as far at 50 m.p.h. as at70 m.p.h. to produce a D.C. feedback voltage at point b equal to Vc. Itcan thus be seen, that by shunting diode 140 and transistor 14S acrossthe feedback potentiometer and by the proper selection of other circuitelements, the D.C. feedback voltage at point b can be made essentiallyequal to V,nl for throttle openings necessary to maintain the idealspeed then attained by the ideal vehicle under ideal conditions.Thereafter, deviations from ideal conditions will cause the vehicle tospeed up or slow down slightly as previously described.

Although we have shown what we consider to be the preferred embodimentof our invention, certain alterations and modifications will becomeapparent to one skilled in the art.

What is claimed is:

1. In a speed control system for automobiles having throttle regulatedpropulsive means, said control system including means for positioningsaid throttle, means responsive to actual automobile speed forgenerating a first feedback electrical signal, means responsive to saidthrottle position for generating a second feedback electrical signal andelectric control means including a memory capacitor and a comparatorwherein said first and second signals are combined with a thirdelectrical signal correlative to a command speed to generate an errorsignal for controlling said throttle positioning means, an improvementcomprising:

memory enabling means having multiple operational modes, a first modecausing a command speed signal derived from and equal to theinstantaneous magnitude of said first signal to be stored in said memorycapacitor, thereby comprising said third electrical signal; and, anacceleration circuit connected to said memory capacitor for overridingsaid first signal in the direction of apparently decreasing automobilespeed when said memory enabling means is in a second mode.

2. A speed control system as recited in claim 1 including a source of areference voltage and wherein:

said comparator includes a high input impedance port vconnected to afirst terminal of said memory capacitor, a second terminal 'beingconnected to said means for generating said first signal;

said acceleration circuit includes an RC network; and

said memory enabling means comprises a switching means which in saidfirst mode connects said memory capacitor first terminal to saidreference voltage source and in said second mode connects said memorycapacitor first terminal to said RC network.

3. A speed control system as recited in claim 2 with additionally:

amplifier means responsive to a disable signal connected between saidcomparator and said throttle positioning means for amplifying said errorsignal;

a source of power for energizing said throttle positioning means;

latching means responsive to a latching signal for latchably connectingsaid power source to said throttle positioning means; and

logic circuitry including a control point and a plurality of logictransistors responsive individually to a control voltage appearing onsaid control point, a first of said logic transistors for applying saidlatching signal to said latching means and a second of said logictransistors for applying said disable signal to said amplifier means.

4. A speed control system as recited in claim 2 with additionally asource of a second reference voltage and wherein said accelerationcircuit comprises:

a capacitor shuntable across said memory capacitor;

and

a resistor switchably connected between said memory capacitor firstterminal yand said source of said second reference voltage.

5. A speed control as recited in claim 4 wherein said memory enablingmeans includes first and second relays comprising first and second coilshaving their input ends capacitively coupled, said first coil input endincluding a means for attenuating a signal applied thereto and first andsecond switch contacts serially connecting said first reference voltagesource to said memory capacitor first terminal, said second switchcontacts being additionally adapted to disconnect said first referencevoltage source and connect said acceleration circuit to said memorycapacitor first terminal and additionally: amplifier means responsive toa disable signal connected 'between said comparator and said throttleposiicning means for amplifying said error signal;

a source of power for energizing said throttle positioning means;

latchng means responsive to a latching signal for latchably connectingsaid power source to said throttle positioning means; and logiccircuitry including:

a control point;

a plurality of logic transistors responsive individually to a controlvoltage appearing on said control point; a first logic transistor whenconductive connecting said power source to said first coil input end andadditionally connecting said power source to said latching means, saidpower source thereby generating said latching signal; a second logictransistor when conductive connecting said power source to said secondcoil input end and additionally connecting said power source to saidamplifier means, said power source thereby generating said amplifierdisable signal.

6. A speed control as recited in claim with additionally a currentresponsive voltage source and means for varying the voltage on saidcontrol point comprising:

means connecting said control point to said voltage source;

a plurality of switches, each having one contact connected to saidcontrol point and the other contact resistively connected to the returncircuit of said voltage source.

7. A speed control system as recited in claim 4 wherein said secondreference voltage source comprises a grounded terminal.

8. A speed control system as recited in claim 4 wherein said memoryenabling -means comprises first and second switch contacts seriallyconnecting said first reference Voltage source to said memory capacitorfirst terminal, said second switch contact being adapted to `disconnectsaid first reference voltage source and connect said accelerationcircuit to said memory capacitor first terminal.

9. A speed control system as recited in claim 8 with additional meansfor opening said second switch contacts after a predetermined time.

10. A speed control system as recited in claim 8 wherein said memoryenabling means additionally includes:

first means for controlling said first switch contacts;

and

second means for controlling said second switch contacts, said secondmeans being adapted to respond with greater sensitivity to an actuatingsignal than said first means.

11. A speed control system as recited in claim 1 with additionally:

a throttle feedback shaping circuit connected between said means forgenerating a second signal and said comparator comprising:

a first electrical path conductive to D.C. components of said throttleposition feedback signal,

a parallel connected second electrical path conductive to A.C.components of said throttle p0- sition feedback signal.

12. In a speed control system as recited in claim 11 wherein saidautomobiles additionally have brakes and brake harness, said controlsystem additionally having:

a source of electrical power;

means responsive to said first electrical signal for generating athreshold signal;

means for generating a latching signal;

latching means dependently responsive to said thresh- 12 y old andlatching signals for connecting said power source to said throttlepositioning means;

first unlatching means responsive to an unlatching signal forinterrupting current flow through said latching means;

means responsive to said brakes for generating a first said unlatchingsignal;

means responsive to the condition of said brake harness for generatingfa second said unlatching signal;

a second unlatching means responsive to said error signal for`interrupting current flow through said latching means,

amplifier means connected between said comparator and said throttlepositioning means for amplifying said error signal;

switching means for disabling said amplifier;

a throttle feedback shaping circuit connected between said means forgenerating a second signal and said comparator having a first electricalpath conductive to throttle feedback components correlative to throttleposition and a second electrical path conductive to throttle feedbackcomponents correlative to speed of throttle movement; and wherein saidmeans for generating a second electrical signal comprises:

a current responsive voltage source;

a potentiometer connected across said voltage source and ganged to saidthrottle;

a transistor responsive to said first electrical signal; and

a diode, said transistor and said diode being connected across saidpotentiometer, the output of said potentiometer 'being connected to saidcomparator through said feedback shaping network.

13. In a speed control system for automobiles having throttle regulatedpropulsive means, an ignition switch, brakes and brake harness, saidcontrol system including means for positioning said throttle, meansresponsive to actual automobile speed for generating a first feedbackelectrical signal, means responsive to said throttle position forgenerating a second feedback electrical signal, means responsive to saidthrottle position for generating a second feedback electrical signal,means for generating a third electrical Signal correlative to a commandspeed and a comparator wherein said first, second and third electricalsignals are combined to generate an error signal for controlling saidmeans for positioning said throttle, an improvement comprising:

a throttle feedback shaping circuit connected between said means forgenerating a second signal and said comparator comprising:

a first electrical path conductive to throttle feedback componentscorrelative to throttle position; and,

a second electrical path conductive to throttle feedback componentscorrelative to speed of throttle movement.

14. A speed control system as recited in claim 13 wherein:

said first electrical path comprises an impedance network having a 0phase angle; and,

said second electrical path comprises an impedance network having anon-0 phase angle.

15. A speed control system as recited in claim 13 wherein said means forgenerating a second signal comprises:

a current responsive voltage source;

a potentiometer connected across said voltage source;

and,

variable impedance means responsive to said first electrical signalconnected across said potentiometer.

16. A speed control system for automobiles having throttle regulatedpropulsive means, said control system including means for positioningsaid throttle, means responsive to actual automobile speed forgenerating a first feedback electrical signal, means responsive tothrottle position for generating a second feedback electrical signal,means for generating a third electrical signal correlative to a commandspeed and a comparator wherein said rst, second, and third electricalsignals are combined to generate an error signal for controlling saidthrottle positioning means wherein said means for generating a secondelectrical signal comprises:

a current responsive voltage source;

a potentiometer connected across said Voltage source,

and ganged to said throttle; and

a transistor responsive to said iirst electrical signal connected acrosssaid potentiometer, the output terminal of said potentiometer beingconnected to said comparator.

17. A speed control system as recited in claim 1'6 wherein said currentresponsive voltage source comprises:

a voltage source;

a rst resistor connected at one end to said voltage source powerterminal; and

a second resistor connected at one end to said voltage source returnterminal, the output of said current responsive voltage source beingtaken across the free ends of said rst and second resistors.

18. A speed control system as recited in claim 17 wherein said iirstresistor differs in value from said second resistor.

19. A speed control system as recited in claim 17 wherein the resistancebetween said potentiometer output terminal and said voltage source powerterminal differs from the resistance between said potentiometer outputterminal and said voltage source return terminal when said throttle isin an idle engine position.

20. A speed control system as recited in claim 17 wherein saidtransistor collector-emitter circuit is connected across saidpotentiometer and said transistor base electrode is connected to saidmeans for generating a first electrical signal and with additionally:

a diode connected in the collector circuit of said transistor;

a third resistor connected between said voltage source power terminaland said transistor collector; means for energizing said throttlepositioning means;

and

latching means responsive to said transistor collector voltage forarming itself and having contacts adapted to switchably connect saidenergizing means to said throttle positioning means;

means for applying a latching signal to said latching means; and

means applying a latching signal to said latching means from saidenergizing means when said contacts are closed.

21. A speed control system for automobiles having throttle regulatedpropulsive means, brakes and a brake harness, said control systemincluding means for positioning said throttle, means responsive toactual automobile speed or generating a rst feedback electrical signal,means responsive to throttle position for generating a second feedbackelectrical signal, means for generating a third electrical signalcorrelative to a command speed and a comparator wherein said iirst,second and third electrical signals are combined to generate an errorsignal for controlling said throttle positioning means, a power source,and self-latching means for switchably applying power to said throttlepositioning means, said latching means comprising:

a latching relay having contacts adapted to switchably connect saidpower source to said throttle positioning means and having one end ofits coil connected to said power source when said contacts are closed;

means responsive to said first electrical signal for generating athreshold signal;

transistor responsive to said threshold signal for connecting the freeend of said coil to the return circuit of said power source to completethe circuit therethrough;

means for applying a latching voltage across said coil;

and

rst unlatching means responsive to an unlatching signal for interruptingthe current through said coil when latched, said threshold signal whenbelow a. threshold value comprising a first unlatching signal.

22. A speed control system as recited in-claim 21 wherein said means forgenerating a threshold signal comprises a dual gain amplifier responsiveto and for amplifying said rst electrical signal, said amplifier outputbeing said threshold signal.

23. A speed control system as claimed in claim 21 with additionally aswitching means ganged to said brakes for applying a second unlatchingsignal to said rst unlatching means.

24. A speed control system as recited in claim 23 wherein said brakeharness comprises a low impedance circuit energized `by said switchingmeans and additionally a high impedance power source for applying athird unlatching signal to said first unlatching mean's when an openfault occurs in said brake harness, said brake harness being normallyconnected to bleed said high impedance power source to a low voltage.

25. A speed control system as recited in claim 24 with additionally:

amplifier means responsive to a disable signal to disable itself andconnected between said comparator and said throttle positioning meansfor amplifying said error signal; and

means coupling said second and third unlatching signals to saidamplifier means, said second and third able signals. unlatching signalsthereby comprising amplier dis- 26. A speed control system as recited inclaim 25 with additionally second unlatching means responsive to apredetermined value of said error signal for interrupting the currentthrough said relay coil.

References Cited UNITED STATES PATENTS 2,980,369 4/1961 Ruof 317-5 X3,060,602 10/ 1962 Buttenhofl 180-105 X 3,070,185 12/1962 Paleis.3,116,807 l/l964 Wilson --109 3,172,497 3/ 1965 Stoner et al. 3,198,9858/1965 Haskell. 3,319,733 5/1967 Rath et al 180-106 3,409,102 ll/ 1968Ncapolitakis et al. 180--109 KENNETH H. BET TS, Primary Examiner U.S.Cl. X.R.

12S- 102; ISO-109; B17-148.5

